Japanese Patent Application Publication No. 2012-190938 discloses an IGBT provided with a rectangular trench. A gate electrode is disposed in the rectangular trench. An emitter region (n-type region), a body contact region (p+-type region), a low-density body region (p−-type region), and the like are provided in a rectangular region (semiconductor region) surrounded by the rectangular trench. The emitter region is in contact with an emitter electrode and the rectangular trench (that is, a gate insulating film). The body contact region is in contact with the emitter electrode. A part of the low-density body region is disposed at a surface portion of a semiconductor substrate, and is in contact with the emitter electrode and the rectangular trench at this location. Further, other parts of the low-density body region are disposed underneath the emitter region and the body contact region, and are in contact with the rectangular trench underneath the emitter region. Further, the semiconductor substrate includes a drift region and a collector region. The drift region is an n-type region disposed underneath the low-density body region. The collector region is a p-type region disposed underneath the drift region. The collector region is in contact with a collector electrode.
When this IGBT turns on, holes flow from the collector electrode to the emitter electrode, and electrons flow from the emitter electrode to the collector electrode. When the holes flow from the drift region into the low-density body region and the like in the rectangular region, the holes flow by avoiding the rectangular trench. Due to this, a hole density in the drift region in a vicinity of the rectangular trench becomes high. Especially in the drift region in a vicinity of connection portions (corner portions) of respective trenches within the rectangular trench, the hole density becomes extremely high since the holes avoiding two trenches flow in high concentration therethrough. Due to this, in the vicinities of the connection portions, a drift region resistance becomes extremely low. Thus, the electrons can flow in the vicinities of the connection portions at low loss. Due to this, this IGBT has a low on-voltage.
Further, Japanese Patent Application Publication No. 2012-190938 discloses a first configuration in which the emitter region is provided at a position being in contact with four trenches of the rectangular trench, and a second configuration in which the emitter region is provided at a position being in contact with two opposing trenches (which are hereinbelow referred to as a first trench and a third trench) of the rectangular trench, and no emitter region is provided at a position being in contact with the other two trenches (which are hereinbelow referred to as a second trench and a fourth trench). In the second configuration, a saturation current of the IGBT becomes smaller as compared to the first configuration. Thus, a short circuiting resistance of the IGBT (time during which the IGBT can withstand short circuiting under a state in which the saturation current is flowing in the IGBT) can be improved.